Cementitious materials, or materials that include cement, e.g., Portland cement, as a binding agent, are commonly used in a variety of building applications including masonry applications. Most common concrete structures and concrete building products formed of such cementitious materials are precast or cast-in-place. Cast-in-place structures typically include walls, curbs, walkways, and flat surfaces such as floors, drives and roads. Cast-in-place refers to the extensive preparation of the site and commonly includes the positioning of various concrete forms. Precast concrete building products, such as barrier or retaining blocks and spanning concrete structures, are commonly formed by pouring a flowable cementitious feed mixture into a form, such as a slip form, which is frequently located remote from the site where the products are actually used. That is, such precast materials are commonly first cast or poured to form a concrete product or article, cured, and then transported to a location where they are used.
While brick, floor and roofing tile, shingles, pavers and curbing can also be precast, efforts have been undertaken in the past to make these concrete products using an extrusion process. While some of these efforts have met with limited commercial success, more widespread commercial acceptance has been lacking because these concrete products often possess drawbacks when compared to their non-concrete counterparts. Controlling the extrusion process to extrude concrete products in a repeatable manner so their properties are consistent from one concrete product to the next has proven challenging. Extruding concrete products that stand up to the elements over time has been another limiting factor. Extruding concrete products that work well in masonry applications has also limited acceptance.
Controlling the repeatability of extruding concrete products so they possess low porosity and high enough strength for their intended application has been extremely challenging. Since concrete products continue to shrink over time, many contractors limit their use only to those applications where such shrinkage will not pose a problem. In addition, since these concrete products typically also possess considerable porosity, especially when compared to their non-concrete counterpart, their tendency to absorb moisture has also limited widespread application. For example, when compared to their non-concrete counterparts, water is absorbed by concrete building products at a much higher rate. Since concrete building products are commonly exposed to the elements, their greater tendency to absorb water is undesirable because the water can seep completely through concrete building products which can result in water damage within the structure formed by the products as well as to the structure itself. Depending on how water saturated concrete building products have become, freeze-thaw cycling can undesirably damage them in a manner that adversely impacts appearance or even their integrity.
One type of commercially available concrete building product that suffers from these and other drawbacks is concrete facing brick used in masonry construction. Concrete facing brick has encountered significant resistance in replacing clay brick for many reasons. It has been difficult to make a concrete facing brick, also known as a concrete masonry unit, having a similar look and feel to that of clay brick because concrete bricks typically lack the texture and coloration of clay bricks. In addition, as a result of concrete bricks continuing to shrink after they have been laid, control joints are required to help control cracking that tends to occur due to shrinkage. Unfortunately, control joints must be sealed with joint sealant with the sealant typically requiring periodic replacement increasing cost. Since concrete bricks are more porous, they typically possess a greater moisture absorption rate than clay brick, which can lead to seepage, structural damage, and loss of brick integrity. These and other drawbacks have significantly limited the commercial acceptance of concrete brick despite being significantly cheaper than clay brick.
What is needed is a machine and method for producing concrete building products having fewer drawbacks than those on the market today. What is also needed is a concrete mixture that is particularly well-suited for making concrete building products having reduced shrinkage and lower moisture absorption. What is also needed is a machine, method and mixture that is capable of being used to make concrete bricks having reduced shrinkage, lower moisture absorption and improved texture and surface characteristics.